A device of the type described in the preamble of claim 1 has the advantage that in quite rapid manner loose packets can be combined into a larger packet by means of strapping with a band which is in fact composed of two parts, the one part end of which is connected to the other part end by a heat weld, and wherein the closing end is likewise realized by a heat weld, during which welding operation the band is held firmly round the packet. This latter requires a rather large tensile force in the band, which tensile force must be produced by the clamping force of the closing jaws, which in turn results in relatively great wear on the guide edges thereof. The known welding jaws moreover have the drawback that when they are retracted some play is released into the band, which causes a reduction in the tensioning force in the band and therefore makes holding together of the strapped packet less stable.